Photothermography (light-sensitive heat-sensitive image formation process) comprises imagewise exposure of a recording material and subsequent uniform heating to develop the exposed recording material. The process is characterized in that images are simply obtained in a single dry process.
Such an image formation process is disclosed in JP-A-52-89915 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"). In this process, a recording material comprising a photopolymerizable composition and heat-sensitive color forming components is subjected to heat development to form a visible image. Specifically, two components of a two-component type heat-sensitive color forming material are provided on a photopolymerizable composition on either the inner side or the outer side thereof, or separately on the inner side and the outer side thereof, to provide a recording material. The recording material thus prepared is exposed to light and heated. As a result, the portion which has been hardened by exposure prevents the heat-sensitive components from reacting such that color is not formed, while the heat-sensitive components in the unexposed portion are mobile upon heating and react to form a color image.
The recording material disclosed in JP-A-61-123838 comprises a photopolymerizable composition consisting of a vinyl monomer containing an acidic group and a photopolymerization initiator, and a dye precursor which produces a dye upon reaction with an acid. In this image formation process, the recording material is imagewise exposed to light and then uniformly heated while being brought into close contact with the dye precursor. The diffused unpolymerized monomer containing an acidic group and the dye precursor react to form an image.
An image formation process disclosed in JP-A-61-120143 comprises imagewise exposing to light a recording material comprising a photohardenable composition, a dye which can be bleached and a bleaching agent which can bleach the dye to cure the exposed portions of the recording material, and then uniformly heating the material to bleach the dye by the reaction of the dye with the bleaching agent in the uncured portions to form an image. As the bleaching agent, a reducing agent or a oxidizing agent is used in the image formation process. Such image formation process is also disclosed in JP-A-60-119552, JP-A-60-120352, JP-A-60-120353 and JP-A-60-120354. In these references, polymerizable vinyl monomer is used as the reducing agent.
Depending on the particular design, these recording materials can use either ultraviolet light or visible light (e.g., visible light laser or LED) as an exposure service.
For recording with ultraviolet light, these recording materials can take the form of either a two sheet transfer type material or preferably a monosheet type material not requiring an extra sheet. However, a monosheet type material cannot be used for recording with visible light.
In order to record with visible light, a colored spectral sensitizer for absorbing visible light and initiating photopolymerization is required. If used in monosheet form, the colored spectral sensitizer remains therein, thereby resulting in an unclear image.